Please refer to FIGS. 1(a) and 1(b), which are the block diagrams of two conventional DC/AC power converters in the prior art respectively.
In FIG. 1(a), the DC/AC power converter 10 includes a SPWM Inverter 101, a Line-Frequency Transformer 102, and a LC Filter 103. Since the Line-Frequency Transformer 102 is employed in transforming a DC input source to an AC output source, the manufacturing cost of this alternative is relatively quite high, and the volume of the DC/AC power converter 10 is relatively bulky.
In FIG. 1(b), the DC/AC power converter 11 includes a High-Frequency Inverter 111, a High-Frequency Transformer 112, a Cycloconverter 113 and a LC Filter 114. Since the High-Frequency Transformer 112 and the Cycloconverter 113 are employed in transforming a DC input source to an AC output source, relatively the manufacturing cost and the weight of the DC/AC power converter 11 of FIG. 1(b) are lower and lighter than those of the DC/AC power converter 10 of FIG. 1(a) respectively. However, the drawbacks of the DC/AC power converter 11 of FIG. 1(b) are that the control circuit thereof is relatively complex and its operational efficiency is relatively low.
Please refer to FIG. 2, it shows the schematic circuit diagram of the conventional current-controlled current source inverter in the prior art. In which, the inverter includes a battery Vin, a transformer Tr, a capacitor C, a load R and five semiconductor switch elements S0-S4.
In which, the semiconductor switch element S0 is located on the primary side of the transformer Tr and is working under the SPWM mode, and the energy in the battery Vin can be transmitted to the load R when the semiconductor switch element S0 is switching.
In FIG. 2, the transformer Tr is a High-Frequency transformer, and has the capability of transmitting the energy. Among the four semiconductor switch elements located on the secondary side of the transformer Tr, S1 to S4, semiconductor switch elements S1 and S3 are working under the working frequency and are switching according to the polarities of the output voltage, and the semiconductor switch elements S2 and S4 are working under the high-frequency while the energy in the load is feedbacked to the battery Vin. The switching of the four semiconductor switch elements, S1 to S4, makes the inverter 20 have the function of two-way energy transmitting.
Relatively, the circuit topology of the inverter 20 has the simpler controlling method, the smaller volume and the lower manufacturing cost, and it would have a relatively better development view in the applications of lower power though. However, the system model of FIG. 2 belongs to buck-boost type circuit topology basically. And the main drawbacks of the inverter 20 are that there are problems regarding the dynamic responses of the whole system are not good when the transformer Tr is working under the CCM mode so as to decrease the voltage stress of the semiconductor switch element S0 and to increase the working efficiency of the inverter 20. Thus, the conventional current-controlled current source inverter 20 of FIG. 2 could not be perfectly applied to the application occasions where relatively larger powers are required.
Keeping the drawbacks of the prior arts in mind, and employing experiments and research full-heartily and persistently, the applicant finally conceived the DC/AC power converter and the controlling method thereof.